In a field such as cell biology, when a specimen solution is irradiated with excitation light such as laser light, fluorescence is generated from a specific fluorescence-stained cell included in the specimen solution. Conventionally, the fluorescence is observed by a fluorescence microscope. However, it has been possible to detect the fluorescence generated from the cell by an optical sensor using a semiconductor.
When the fluorescence generated from the cell in the specimen solution is detected by the optical sensor, if the excitation light directly enters the optical sensor, or if the excitation light is reflected by a wiring in the optical sensor and enters the optical sensor, such light is detected as a noise. Thus, it is difficult to detect the fluorescence from a specimen with high sensitivity, due to the noise.
Accordingly, it is desired to provide an optical sensor capable of preventing a noise from generating, to detect fluorescence from a specimen with high sensitivity.